Many machines use multiple hydraulic actuators to accomplish a variety of tasks. Examples of such machines include without limitation dozers, loaders, excavators, motor graders, and other types of heavy machinery. The hydraulic actuators in such machines are linked via fluid flow lines to a pump associated with the machine to provide pressurized fluid to the hydraulic actuators. Chambers within the various actuators receive the pressurized fluid in controlled flow rates and/or pressures in response to operator demands or other signals. Although most such machines are deigned to allow multiple actuators to be used simultaneously, in certain circumstances the demanded fluid flow will exceed the output capabilities of the fluid pump, especially when a single such pump is used. In the event that a flow of fluid supplied to one of the actuators is less than what is demanded by the machine operator or control system, the affected actuator may respond too slowly, too gently, or otherwise behave in an unexpected manner.
Given this problem, various solutions have evolved in the art. One method of accommodating a demand for fluid flow that is greater than the capacity of an associated pump is described in U.S. Appl. 20060090459 by Devier et al. entitled “Hydraulic System Having Priority Based Flow Control” (“the '459 application”). The '459 application describes a hydraulic system controller that is configured to receive input indicative classifying a plurality of fluid actuators as being either of a first or a second type. When an input indicative of a desired flow rate for the plurality of fluid actuators is received, the controller determines a current flow rate of the source. If all demanded flow rates can be met, the controller demands this amount of flow. Otherwise, the controller demands the desired flow rate only for the first type of fluid actuator and scales down the desired flow rate for the second type of fluid actuator. When the desired flow rate just for the first type of fluid actuators alone exceeds the current flow rate of the source, the controller scales down the desired flow rate for all of the fluid actuators. Thus there are three regimes in which the controller of the '459 application operates.
The disclosed hydraulic system is directed to overcoming one or more of the problems set forth above. It should be appreciated that the foregoing background discussion is intended solely to aid the reader. It is not intended to limit the disclosure or claims, and thus should not be taken to indicate that any particular element of a prior system is unsuitable for use, nor is it intended to indicate any element, including solving the motivating problem, to be essential in implementing the examples described herein or similar examples.